North Korea warns its military allowed to wage nuke strikes against US

U.S. officials tell NBC News they believe North Korea does have the capability to put a nuclear weapon on a missile and that they have missile deliverable nukes. Those missiles, however, cannot go more than 1000 miles. NBC's Richard Engel reports.

By Alastair Jamieson, Jim Miklaszewski and Courtney Kube, NBC News

North Korea escalated its provocative rhetoric on Thursday, warning that its military is authorized to wage "cutting-edge smaller, lighter and diversified" nuclear strikes to protect against the United States.

"The moment of explosion is approaching fast. No one can say a war will break out in Korea or not and whether it will break out today or tomorrow," read the statement of an unnamed military spokesman.

The statement, which was carried by the state-run Korean Central News Agency (KCNA), informs the White House and the Pentagon that "the merciless operation of its revolutionary armed forces in this regard has been finally examined and ratified."

The warlike rhetoric is the latest escalation in a series of threats from Pyongyang, which claims the joint U.S. and South Korean military exercises taking place in the South are in preparation for an invasion.

"The U.S. high-handed hostile policy toward the DPRK aimed to encroach upon its sovereignty and the dignity of its supreme leadership and bring down its social system is being implemented through actual military actions without hesitation," the military statement read.

The United States says the exercises are routine military drills.

Defense Secretary Chuck Hagel said Wednesday that North Korea's provocations are "a real and clear danger and threat" to U.S. interests and Washington is taking them seriously.

U.S. Secretary of Defense Chuck Hagel addresses the ongoing threats made by the North Korean government while speaking Wednesday.

"We are doing everything we can ... to defuse that situation on the peninsula," Hagel said after a speech at the National Defense University at Fort McNair in Washington, D.C.

"I hope the North will ratchet this very dangerous rhetoric down," he said, adding that there is a pathway to peace but only if Pyongyang decides to be "a responsible member of the world community."

U.S. response

The U.S. has responded to the diplomatic crisis with more than words, dispatching two warships to the western Pacific to be on alert for missiles and conducting bomber and fighter flyovers.

Defense officials also said an advanced anti-ballistic missile system will be sent to the U.S. military base in Guam in response to North Korean threats targeting Guam and U.S. military facilities in the region.

The system -- which includes missiles, launchers, radar and communications -- is expected to arrive within two weeks.

A former UN official who visited North Korea last year reports that officials there said they could re-start the Yongbyon reactor in three months.

That is a lot shorter than many U.S. nuclear experts believe a re-start would take.

U.S. officials tell NBC News that no matter what the timeline is, they don't believe the operation would be a huge engineering challenge. A re-start would, however, be significant, as it would give North Korea the capability to make weapons-grade plutonium again. The reactor was shut down in 2007.

"North Korea's assertion that it intends to bring Yongbyon back on line can't be easily written off as an insurmountable hurdle," said one U.S. official.

If North Korea were to employ nuclear weapons, it would impact U.S. troops and pressure Japan and South Korea to also consider obtaining nuclear weapons – something that could lead to an all-out arms race. NBC's Andrea Mitchell reports.

Asked how long a re-start might take, U.S. intelligence officials declined to provide any details.

Banning South Korean workersNorth Korean leader Kim Jong Un has shown no inclination to back off yet. The rogue nuclear state's latest move was banning South Korean workers from the jointly run Kaesong industrial zone.

Seoul said about 800 South Koreans who had stayed overnight at the complex were being allowed to return home, but that new workers were not being allowed across the border.

"South Korea's government deeply regrets the entry ban and urges it be lifted immediately," South Korea official Kim Hyung-seok told reporters Wednesday.

China expressed "serious concern" to U.S. diplomats over the worsening crisis. A Chinese official met ambassadors from the United States and both Koreas, expressing hope that Pyongyang and Seoul could resolve their differences through talks, China’s foreign ministry spokesman Hong Lei said, according to Reuters and Voice of America reporter Steve Herman.

Vowing to reopen the Yongbyong nuclear reactor, North Korean dictator Kim Jong Un showed no sign he's listening to the outside world and that his nation has no intention of giving up its nuclear weapons. NBC's Richard Engel reports.

The comments came after Secretary of State John Kerry denounced North Korea's increasingly threatening rhetoric as "unacceptable," and said the U.S. would defend its allies, South Korea and Japan, from any threat from the North.

During a joint news conference with South Korea's foreign minister at the State Department on Tuesday, Kerry said North Korea knows what it needs to do if it wants to resume dialogue with the rest of the world.